1. Field of the Invention
The present invention relates to an image display device and an image display method for displaying an image with the image being changed according to an observer's viewing direction.
2. Related Background of the Invention
There is known a display technique of images for controlling a light source which is visible from an observer by disposing a shielding such as a parallax barrier, or an optical element such as a lenticular sheet or a lens array in front of a light source array such as a liquid crystal display. The display technique produces parallax since the observed image varies according to the position of the observer. Since the technique realizes binocular parallax when both eyes are used for observation, it is applied to a three dimensional (3D) display, as well as an image display device which can provide different images to be observed for respective observers, for example, when the same display is observed from a driver's seat and a passenger's seat in a car.
FIG. 1 illustrates an exemplary display using a parallax barrier, and FIG. 2 illustrates an exemplary display using a lenticular sheet. In FIGS. 1 and 2, the display includes a light source array (light sources 1 to 8), the light source array corresponding to each pixel of the liquid crystal display, for example. FIGS. 1 and 2 show that light emitted from the light sources 1, 3 and 5 is visible from respective directions of the corresponding arrows. Although other light sources are not illustrated, they are similarly visible from the respective corresponding angular directions. In any of the techniques, an area in which each light source array is visible is limited, thereby allowing a three-dimensional image to be displayed by producing binocular parallax. The display shown in FIGS. 1 and 2 is an example of a four-view display, however a stereo display (two-view) and a multi-view display for displaying multi-view images are similar in principle.
There is also a method which allows different images to be visible according to the viewing position, when seen from above, beneath, right, or left, by replacing the lenticular sheet of FIG. 2 with a microlens array and controlling the direction of the light emitted from the light source similarly along the vertical direction, which is referred to as integral photography (IP).
When displaying different images according to the observation position by placing, in front of the light source array (output plane of the light source), for example, a parallax barrier 10 having periodically repetitive slits, or a light beam control element such as a lenticular sheet 11 or a lens array to produce parallax, the above-mentioned light beam control element controls the observer's viewing area for several light source arrays to realize multi-view (including two-view, i.e., stereo vision) display. For example, in the case of a four-view display, a slit or a cylindrical lens constituting the lenticular sheet is provided for four light sources (i.e., four pixels), and the slits or the cylindrical lenses control the area in which the observer can view the light emitted from the light source.
A set of the four light sources, when used as a 3D display which is a fundamental application of these devices, is referred to as a 3D pixel, since the set is a minimal unit of a 3D image when displaying the 3D image. With the conventional method using a parallax barrier, a lenticular sheet, or a lens array, there exists an area for each of the 3D pixels in which a 3D image can be normally observed.
FIG. 3 is an explanatory view illustrating the area in which a 3D image can be observed when a lenticular sheet is used. As shown in FIG. 3, the output direction of the light is changed by the action of the cylindrical lens constituting the lenticular sheet 11 for the 3D pixels (light sources 5 to 8), so that an area in which the light is visible, i.e., viewing area is produced. In addition, the parallax barrier method is similar in principle, except that the disposed lenticular sheet is an element for periodically providing a shield and an opening in repetition (see FIG. 1).
Also with the IP method, although the shape of the cross section is similar to that of FIG. 3, the cross section is similar along the vertical direction, since the light beam control element is not a lenticular sheet but a lens array, and thereby the 3D pixel b is formed by a set of light sources which are two-dimensionally disposed. FIG. 4 is an explanatory view illustrating a case using a nine-view IP method composed of a vertically three-parallax 3D pixel b1 and a horizontally three-parallax 3D pixel b2. With regard to the arrows indicating the viewing direction of the light source, only those corresponding to three vertical parallaxes in the middle are shown in FIG. 4. However, the lenticular sheet 11 which is the light beam control element similarly controls the parallaxes along nine directions vertically and horizontally.
As stated above, the techniques of varying the image to be displayed according to position of the observer include, for example, patent literature 1 (Japanese Patent Application No. 7-270745) and patent literature 2 (Japanese Patent Application Laid-Open No. 2002-296540). The techniques described in patent literatures 1 and 2 relate to a 3D image display device, wherein 3D images can be displayed by displaying pixels for the left eye and pixels for the right eye, and images according to the position of the observer can be displayed by turning the barrier on and off.
[Patent Literature 1] Japanese Patent Application Laid-Open No. 7-270745
[Patent Literature 2] Japanese Patent Application Laid-Open No. 2002-296540